I have some really strong emotional feelings about fluid bonding. Although trust is part of it, it's..you know, it's actually slightly embarrassing to put into words, but there is a feeling of if a person is coming inside me, then they're kind of becoming a part of me (and vice versa, with my fluids being on them long enough to "infuse" into them). There aren't necessarily a lot of people who I want to have that sharing with, on that level.
When Jon was dating both Lora and I, he was fluid-bonded to her, and eventually to me. For her it was a practical "I don't want to get STIs from a metamour" thing, so she was cautious and needed a lot of talking and thinking to be OK with it. For Jon, it was both that, and emotional feelings too.
During that time, I was only fluid-bonded to Jon. Now that Jon is not with Lora anymore, we're only fluid-bonded to each other.
I would be comfortable with either of us being fluid-bonded to another person (maybe even two, probably won't know until/unless it happens!), but I would definitely want to know that that person is also being safe and using condoms with most other partners. I'm not sure how I'd feel if I met someone who I wanted to be fluid-bonded with who was part of a "chain" of fluid-bonded people (like if he/she was also fluid-bonded to one other person, who was fluid-bonded to that person and one other person who was also only fluid bonded to two other people, but continuing on and on). I think it would depend on how long the chain went on.
I'd feel the same way about Jon wanting to fluid bond to someone who was part of a chain, but I have a feeling that he'd be more likely to be extremely cautious about it than I would. He is very slow about becoming sexually intimate with people to begin with, so I think becoming part of a chain of fluid-bonded people would really make him nervous.
FTR, we do always use condoms with anal still, because...bacteria is bad, you know?